Caching systems and methods

ABSTRACT

Example caching systems and methods are described. In one implementation, a method identifies multiple files used to process a query and distributes each of the multiple files to a particular execution node to execute the query. Each execution node determines whether the distributed file is stored in the execution node&#39;s cache. If the execution node determines that the file is stored in the cache, it processes the query using the cached file. If the file is not stored in the cache, the execution node retrieves the file from a remote storage device, stores the file in the execution node&#39;s cache, and processes the query using the file.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/941,986, entitled “Apparatus and method for enterprise datawarehouse data processing on cloud infrastructure,” filed Feb. 19, 2014,the disclosure of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to resource management systems andmethods that manage the caching of data.

BACKGROUND

Many existing data storage and retrieval systems are available today.For example, in a shared-disk system, all data is stored on a sharedstorage device that is accessible from all of the processing nodes in adata cluster. In this type of system, all data changes are written tothe shared storage device to ensure that all processing nodes in thedata cluster access a consistent version of the data. As the number ofprocessing nodes increases in a shared-disk system, the shared storagedevice (and the communication links between the processing nodes and theshared storage device) becomes a bottleneck that slows data read anddata write operations. This bottleneck is further aggravated with theaddition of more processing nodes. Thus, existing shared-disk systemshave limited scalability due to this bottleneck problem.

Another existing data storage and retrieval system is referred to as a“shared-nothing architecture.” In this architecture, data is distributedacross multiple processing nodes such that each node stores a subset ofthe data in the entire database. When a new processing node is added orremoved, the shared-nothing architecture must rearrange data across themultiple processing nodes. This rearrangement of data can betime-consuming and disruptive to data read and write operations executedduring the data rearrangement. And, the affinity of data to a particularnode can create “hot spots” on the data cluster for popular data.Further, since each processing node performs also the storage function,this architecture requires at least one processing node to store data.Thus, the shared-nothing architecture fails to store data if allprocessing nodes are removed. Additionally, management of data in ashared-nothing architecture is complex due to the distribution of dataacross many different processing nodes.

The systems and methods described herein provide an improved approach todata storage and data retrieval that alleviates the above-identifiedlimitations of existing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various figuresunless otherwise specified.

FIG. 1 is a block diagram depicting an example embodiment of the systemsand methods described herein.

FIG. 2 is a block diagram depicting an embodiment of a resource manager.

FIG. 3 is a block diagram depicting an embodiment of an executionplatform.

FIG. 4 is a block diagram depicting an example operating environmentwith multiple users accessing multiple databases through multiplevirtual warehouses.

FIG. 5 is a block diagram depicting another example operatingenvironment with multiple users accessing multiple databases through aload balancer and multiple virtual warehouses contained in a virtualwarehouse group.

FIG. 6 is a block diagram depicting another example operatingenvironment having multiple distributed virtual warehouses and virtualwarehouse groups.

FIG. 7 is a flow diagram depicting an embodiment of a method formanaging data storage and retrieval operations.

FIG. 8 is a flow diagram depicting an embodiment of a method formanaging a data cache.

FIG. 9 is a block diagram depicting an example computing device.

DETAILED DESCRIPTION

The systems and methods described herein provide a new platform forstoring and retrieving data without the problems faced by existingsystems. For example, this new platform supports the addition of newnodes without the need for rearranging data files as required by theshared-nothing architecture. Additionally, nodes can be added to theplatform without creating bottlenecks that are common in the shared-disksystem. This new platform is always available for data read and datawrite operations, even when some of the nodes are offline formaintenance or have suffered a failure. The described platform separatesthe data storage resources from the computing resources so that data canbe stored without requiring the use of dedicated computing resources.This is an improvement over the shared-nothing architecture, which failsto store data if all computing resources are removed. Therefore, the newplatform continues to store data even though the computing resources areno longer available or are performing other tasks.

In the following description, reference is made to the accompanyingdrawings that form a part thereof, and in which is shown by way ofillustration specific exemplary embodiments in which the disclosure maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the concepts disclosedherein, and it is to be understood that modifications to the variousdisclosed embodiments may be made, and other embodiments may beutilized, without departing from the scope of the present disclosure.The following detailed description is, therefore, not to be taken in alimiting sense.

Reference throughout this specification to “one embodiment,” “anembodiment,” “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thepresent disclosure. Thus, appearances of the phrases “in oneembodiment,” “in an embodiment,” “one example” or “an example” invarious places throughout this specification are not necessarily allreferring to the same embodiment or example. In addition, it should beappreciated that the figures provided herewith are for explanationpurposes to persons ordinarily skilled in the art and that the drawingsare not necessarily drawn to scale.

Embodiments in accordance with the present disclosure may be embodied asan apparatus, method or computer program product. Accordingly, thepresent disclosure may take the form of an entirely hardware-comprisedembodiment, an entirely software-comprised embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,embodiments of the present disclosure may take the form of a computerprogram product embodied in any tangible medium of expression havingcomputer-usable program code embodied in the medium.

Any combination of one or more computer-usable or computer-readablemedia may be utilized. For example, a computer-readable medium mayinclude one or more of a portable computer diskette, a hard disk, arandom access memory (RAM) device, a read-only memory (ROM) device, anerasable programmable read-only memory (EPROM or Flash memory) device, aportable compact disc read-only memory (CDROM), an optical storagedevice, and a magnetic storage device. Computer program code forcarrying out operations of the present disclosure may be written in anycombination of one or more programming languages. Such code may becompiled from source code to computer-readable assembly language ormachine code suitable for the device or computer on which the code willbe executed.

Embodiments may also be implemented in cloud computing environments. Inthis description and the following claims, “cloud computing” may bedefined as a model for enabling ubiquitous, convenient, on-demandnetwork access to a shared pool of configurable computing resources(e.g., networks, servers, storage, applications, and services) that canbe rapidly provisioned via virtualization and released with minimalmanagement effort or service provider interaction and then scaledaccordingly. A cloud model can be composed of various characteristics(e.g., on-demand self-service, broad network access, resource pooling,rapid elasticity, and measured service), service models (e.g., Softwareas a Service (“SaaS”), Platform as a Service (“PaaS”), andInfrastructure as a Service (“IaaS”)), and deployment models (e.g.,private cloud, community cloud, public cloud, and hybrid cloud).

The flow diagrams and block diagrams in the attached figures illustratethe architecture, functionality, and operation of possibleimplementations of systems, methods, and computer program productsaccording to various embodiments of the present disclosure. In thisregard, each block in the flow diagrams or block diagrams may representa module, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It will also be noted that each block of the block diagramsand/or flow diagrams, and combinations of blocks in the block diagramsand/or flow diagrams, may be implemented by special purposehardware-based systems that perform the specified functions or acts, orcombinations of special purpose hardware and computer instructions.These computer program instructions may also be stored in acomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instruction meanswhich implement the function/act specified in the flow diagram and/orblock diagram block or blocks.

The systems and methods described herein provide a flexible and scalabledata warehouse using a new data processing platform. In someembodiments, the described systems and methods leverage a cloudinfrastructure that supports cloud-based storage resources, computingresources, and the like. Example cloud-based storage resources offersignificant storage capacity available on-demand at a low cost. Further,these cloud-based storage resources may be fault-tolerant and highlyscalable, which can be costly to achieve in private data storagesystems. Example cloud-based computing resources are available on-demandand may be priced based on actual usage levels of the resources.Typically, the cloud infrastructure is dynamically deployed,reconfigured, and decommissioned in a rapid manner.

In the described systems and methods, a data storage system utilizes anSQL (Structured Query Language)-based relational database. However,these systems and methods are applicable to any type of database, andany type of data storage and retrieval platform, using any data storagearchitecture and using any language to store and retrieve data withinthe data storage and retrieval platform. The systems and methodsdescribed herein further provide a multi-tenant system that supportsisolation of computing resources and data between differentcustomers/clients and between different users within the samecustomer/client.

FIG. 1 is a block diagram depicting an example embodiment of a new dataprocessing platform 100. As shown in FIG. 1 , a resource manager 102 iscoupled to multiple users 104, 106, and 108. In particularimplementations, resource manager 102 can support any number of usersdesiring access to data processing platform 100. Users 104-108 mayinclude, for example, end users providing data storage and retrievalrequests, system administrators managing the systems and methodsdescribed herein, and other components/devices that interact withresource manager 102. Resource manager 102 provides various services andfunctions that support the operation of all systems and componentswithin data processing platform 100. As used herein, resource manager102 may also be referred to as a “global services system” that performsvarious functions as discussed herein.

Resource manager 102 is also coupled to metadata 110, which isassociated with the entirety of data stored throughout data processingplatform 100. In some embodiments, metadata 110 includes a summary ofdata stored in remote data storage systems as well as data availablefrom a local cache. Additionally, metadata 110 may include informationregarding how data is organized in the remote data storage systems andthe local caches. Metadata 110 allows systems and services to determinewhether a piece of data needs to be accessed without loading oraccessing the actual data from a storage device.

Resource manager 102 is further coupled to an execution platform 112,which provides multiple computing resources that execute various datastorage and data retrieval tasks, as discussed in greater detail below.Execution platform 112 is coupled to multiple data storage devices 116,118, and 120 that are part of a storage platform 114. Although threedata storage devices 116, 118, and 120 are shown in FIG. 1 , executionplatform 112 is capable of communicating with any number of data storagedevices. In some embodiments, data storage devices 116, 118, and 120 arecloud-based storage devices located in one or more geographic locations.For example, data storage devices 116, 118, and 120 may be part of apublic cloud infrastructure or a private cloud infrastructure. Datastorage devices 116, 118, and 120 may be hard disk drives (HDDs), solidstate drives (SSDs), storage clusters, Amazon S3™ storage systems or anyother data storage technology. Additionally, storage platform 114 mayinclude distributed file systems (such as Hadoop Distributed FileSystems (HDFS)), object storage systems, and the like.

In particular embodiments, the communication links between resourcemanager 102 and users 104-108, metadata 110, and execution platform 112are implemented via one or more data communication networks. Similarly,the communication links between execution platform 112 and data storagedevices 116-120 in storage platform 114 are implemented via one or moredata communication networks. These data communication networks mayutilize any communication protocol and any type of communication medium.In some embodiments, the data communication networks are a combinationof two or more data communication networks (or sub-networks) coupled toone another. In alternate embodiments, these communication links areimplemented using any type of communication medium and any communicationprotocol.

As shown in FIG. 1 , data storage devices 116, 118, and 120 aredecoupled from the computing resources associated with executionplatform 112. This architecture supports dynamic changes to dataprocessing platform 100 based on the changing data storage/retrievalneeds as well as the changing needs of the users and systems accessingdata processing platform 100. The support of dynamic changes allows dataprocessing platform 100 to scale quickly in response to changing demandson the systems and components within data processing platform 100. Thedecoupling of the computing resources from the data storage devicessupports the storage of large amounts of data without requiring acorresponding large amount of computing resources. Similarly, thisdecoupling of resources supports a significant increase in the computingresources utilized at a particular time without requiring acorresponding increase in the available data storage resources.

Resource manager 102, metadata 110, execution platform 112, and storageplatform 114 are shown in FIG. 1 as individual components. However, eachof resource manager 102, metadata 110, execution platform 112, andstorage platform 114 may be implemented as a distributed system (e.g.,distributed across multiple systems/platforms at multiple geographiclocations). Additionally, each of resource manager 102, metadata 110,execution platform 112, and storage platform 114 can be scaled up ordown (independently of one another) depending on changes to the requestsreceived from users 104-108 and the changing needs of data processingplatform 100. Thus, in the described embodiments, data processingplatform 100 is dynamic and supports regular changes to meet the currentdata processing needs.

During typical operation, data processing platform 100 processesmultiple queries (or requests) received from any of the users 104-108.These queries are managed by resource manager 102 to determine when andhow to execute the queries. For example, resource manager 102 maydetermine what data is needed to process the query and further determinewhich nodes within execution platform 112 are best suited to process thequery. Some nodes may have already cached the data needed to process thequery and, therefore, are good candidates for processing the query.Metadata 110 assists resource manager 102 in determining which nodes inexecution platform 112 already cache at least a portion of the dataneeded to process the query. One or more nodes in execution platform 112process the query using data cached by the nodes and, if necessary, dataretrieved from storage platform 114. It is desirable to retrieve as muchdata as possible from caches within execution platform 112 because theretrieval speed is typically much faster than retrieving data fromstorage platform 114.

As shown in FIG. 1 , data processing platform 100 separates executionplatform 112 from storage platform 114. In this arrangement, theprocessing resources and cache resources in execution platform 112operate independently of the data storage resources 116-120 in storageplatform 114. Thus, the computing resources and cache resources are notrestricted to specific data storage resources 116-120. Instead, allcomputing resources and all cache resources may retrieve data from, andstore data to, any of the data storage resources in storage platform114. Additionally, data processing platform 100 supports the addition ofnew computing resources and cache resources to execution platform 112without requiring any changes to storage platform 114. Similarly, dataprocessing platform 100 supports the addition of data storage resourcesto storage platform 114 without requiring any changes to nodes inexecution platform 112.

FIG. 2 is a block diagram depicting an embodiment of resource manager102. As shown in FIG. 2 , resource manager 102 includes an accessmanager 202 and a key manager 204 coupled to a data storage device 206.Access manager 202 handles authentication and authorization tasks forthe systems described herein. Key manager 204 manages storage andauthentication of keys used during authentication and authorizationtasks. For example, access manager 202 and key manager 204 manage thekeys used to access data stored in remote storage devices (e.g., datastorage devices in storage platform 114). As used herein, the remotestorage devices may also be referred to as “persistent storage devices.”A request processing service 208 manages received data storage requestsand data retrieval requests (e.g., database queries). For example,request processing service 208 may determine the data necessary toprocess the received data storage request or data retrieval request. Thenecessary data may be stored in a cache within execution platform 112(as discussed in greater detail below) or in a data storage device instorage platform 114. A management console service 210 supports accessto various systems and processes by administrators and other systemmanagers. Additionally, management console service 210 may receiverequests from users 104-108 to issue queries and monitor the workload onthe system. In some embodiments, a particular user may issue a requestto monitor the workload that their specific query places on the system.

Resource manager 102 also includes an SQL compiler 212, an SQL optimizer214 and an SQL executor 210. SQL compiler 212 parses SQL queries andgenerates the execution code for the queries. SQL optimizer 214determines the best method to execute queries based on the data thatneeds to be processed. SQL optimizer 214 also handles various datapruning operations and other data optimization techniques to improve thespeed and efficiency of executing the SQL query. SQL executor 216executes the query code for queries received by resource manager 102.

A query scheduler and coordinator 218 sends received queries to theappropriate services or systems for compilation, optimization, anddispatch to execution platform 112. For example, queries may beprioritized and processed in that prioritized order. In someembodiments, query scheduler and coordinator 218 identifies or assignsparticular nodes in execution platform 112 to process particularqueries. A virtual warehouse manager 220 manages the operation ofmultiple virtual warehouses implemented in execution platform 112. Asdiscussed below, each virtual warehouse includes multiple executionnodes that each include a cache and a processor.

Additionally, resource manager 102 includes a configuration and metadatamanager 222, which manages the information related to the data stored inthe remote data storage devices and in the local caches (i.e., thecaches in execution platform 112). As discussed in greater detail below,configuration and metadata manager 222 uses the metadata to determinewhich data files need to be accessed to retrieve data for processing aparticular query. A monitor and workload analyzer 224 oversees theprocesses performed by resource manager 102 and manages the distributionof tasks (e.g., workload) across the virtual warehouses and executionnodes in execution platform 112. Monitor and workload analyzer 224 alsoredistributes tasks, as needed, based on changing workloads throughoutdata processing platform 100. Configuration and metadata manager 222 andmonitor and workload analyzer 224 are coupled to a data storage device226. Data storage devices 206 and 226 in FIG. 2 represent any datastorage device within data processing platform 100. For example, datastorage devices 206 and 226 may represent caches in execution platform112, storage devices in storage platform 114, or any other storagedevice.

Resource manager 102 also includes a transaction management and accesscontrol module 228, which manages the various tasks and other activitiesassociated with the processing of data storage requests and data accessrequests. For example, transaction management and access control module228 provides consistent and synchronized access to data by multipleusers or systems. Since multiple users/systems may access the same datasimultaneously, changes to the data must be synchronized to ensure thateach user/system is working with the current version of the data.Transaction management and access control module 228 provides control ofvarious data processing activities at a single, centralized location inresource manager 102. In some embodiments, transaction management andaccess control module 228 interacts with SQL executor 216 to support themanagement of various tasks being executed by SQL executor 216.

FIG. 3 is a block diagram depicting an embodiment of an executionplatform 112. As shown in FIG. 3 , execution platform 112 includesmultiple virtual warehouses 302, 304, and 306. Each virtual warehouseincludes multiple execution nodes that each include a data cache and aprocessor. Virtual warehouses 302, 304, and 306 are capable of executingmultiple queries (and other tasks) in parallel by using the multipleexecution nodes. As discussed herein, execution platform 112 can add newvirtual warehouses and drop existing virtual warehouses in real timebased on the current processing needs of the systems and users. Thisflexibility allows execution platform 112 to quickly deploy largeamounts of computing resources when needed without being forced tocontinue paying for those computing resources when they are no longerneeded. All virtual warehouses can access data from any data storagedevice (e.g., any storage device in storage platform 114).

Although each virtual warehouse 302-306 shown in FIG. 3 includes threeexecution nodes, a particular virtual warehouse may include any numberof execution nodes. Further, the number of execution nodes in a virtualwarehouse is dynamic, such that new execution nodes are created whenadditional demand is present, and existing execution nodes are deletedwhen they are no longer necessary.

Each virtual warehouse 302-306 is capable of accessing any of the datastorage devices 116-120 shown in FIG. 1 . Thus, virtual warehouses302-306 are not necessarily assigned to a specific data storage device116-120 and, instead, can access data from any of the data storagedevices 116-120. Similarly, each of the execution nodes shown in FIG. 3can access data from any of the data storage devices 116-120. In someembodiments, a particular virtual warehouse or a particular executionnode may be temporarily assigned to a specific data storage device, butthe virtual warehouse or execution node may later access data from anyother data storage device.

In the example of FIG. 3 , virtual warehouse 302 includes threeexecution nodes 308, 310, and 312. Execution node 308 includes a cache314 and a processor 316. Execution node 310 includes a cache 318 and aprocessor 320. Execution node 312 includes a cache 322 and a processor324. Each execution node 308-312 is associated with processing one ormore data storage and/or data retrieval tasks. For example, a particularvirtual warehouse may handle data storage and data retrieval tasksassociated with a particular user or customer. In other implementations,a particular virtual warehouse may handle data storage and dataretrieval tasks associated with a particular data storage system or aparticular category of data.

Similar to virtual warehouse 302 discussed above, virtual warehouse 304includes three execution nodes 326, 328, and 330. Execution node 326includes a cache 332 and a processor 334. Execution node 328 includes acache 336 and a processor 338. Execution node 330 includes a cache 340and a processor 342. Additionally, virtual warehouse 306 includes threeexecution nodes 344, 346, and 348. Execution node 344 includes a cache350 and a processor 352. Execution node 346 includes a cache 354 and aprocessor 356. Execution node 348 includes a cache 358 and a processor360.

In some embodiments, the execution nodes shown in FIG. 3 are statelesswith respect to the data the execution nodes are caching. For example,these execution nodes do not store or otherwise maintain stateinformation about the execution node or the data being cached by aparticular execution node. Thus, in the event of an execution nodefailure, the failed node can be transparently replaced by another node.Since there is no state information associated with the failed executionnode, the new (replacement) execution node can easily replace the failednode without concern for recreating a particular state.

Although the execution nodes shown in FIG. 3 each include one data cacheand one processor, alternate embodiments may include execution nodescontaining any number of processors and any number of caches.Additionally, the caches may vary in size among the different executionnodes. The caches shown in FIG. 3 store, in the local execution node,data that was retrieved from one or more data storage devices in storageplatform 114 (FIG. 1 ). Thus, the caches reduce or eliminate thebottleneck problems occurring in platforms that consistently retrievedata from remote storage systems. Instead of repeatedly accessing datafrom the remote storage devices, the systems and methods describedherein access data from the caches in the execution nodes which issignificantly faster and avoids the bottleneck problem discussed above.In some embodiments, the caches are implemented using high-speed memorydevices that provide fast access to the cached data. Each cache canstore data from any of the storage devices in storage platform 114.

Further, the cache resources and computing resources may vary betweendifferent execution nodes. For example, one execution node may containsignificant computing resources and minimal cache resources, making theexecution node useful for tasks that require significant computingresources. Another execution node may contain significant cacheresources and minimal computing resources, making this execution nodeuseful for tasks that require caching of large amounts of data. Yetanother execution node may contain cache resources providing fasterinput-output operations, useful for tasks that require fast scanning oflarge amounts of data. In some embodiments, the cache resources andcomputing resources associated with a particular execution node aredetermined when the execution node is created, based on the expectedtasks to be performed by the execution node.

Additionally, the cache resources and computing resources associatedwith a particular execution node may change over time based on changingtasks performed by the execution node. For example, a particularexecution node may be assigned more processing resources if the tasksperformed by the execution node become more processor intensive.Similarly, an execution node may be assigned more cache resources if thetasks performed by the execution node require a larger cache capacity.

Although virtual warehouses 302-306 are associated with the sameexecution platform 112, the virtual warehouses may be implemented usingmultiple computing systems at multiple geographic locations. Forexample, virtual warehouse 302 can be implemented by a computing systemat a first geographic location, while virtual warehouses 304 and 306 areimplemented by another computing system at a second geographic location.In some embodiments, these different computing systems are cloud-basedcomputing systems maintained by one or more different entities.

Additionally, each virtual warehouse is shown in FIG. 3 as havingmultiple execution nodes. The multiple execution nodes associated witheach virtual warehouse may be implemented using multiple computingsystems at multiple geographic locations. For example, a particularinstance of virtual warehouse 302 implements execution nodes 308 and 310on one computing platform at a particular geographic location, andimplements execution node 312 at a different computing platform atanother geographic location. Selecting particular computing systems toimplement an execution node may depend on various factors, such as thelevel of resources needed for a particular execution node (e.g.,processing resource requirements and cache requirements), the resourcesavailable at particular computing systems, communication capabilities ofnetworks within a geographic location or between geographic locations,and which computing systems are already implementing other executionnodes in the virtual warehouse.

Execution platform 112 is also fault tolerant. For example, if onevirtual warehouse fails, that virtual warehouse is quickly replaced witha different virtual warehouse at a different geographic location.

A particular execution platform 112 may include any number of virtualwarehouses 302-306. Additionally, the number of virtual warehouses in aparticular execution platform is dynamic, such that new virtualwarehouses are created when additional processing and/or cachingresources are needed. Similarly, existing virtual warehouses may bedeleted when the resources associated with the virtual warehouse are nolonger necessary.

In some embodiments, virtual warehouses 302, 304, and 306 may operate onthe same data in storage platform 114, but each virtual warehouse hasits own execution nodes with independent processing and cachingresources. This configuration allows requests on different virtualwarehouses to be processed independently and with no interferencebetween the requests. This independent processing, combined with theability to dynamically add and remove virtual warehouses, supports theaddition of new processing capacity for new users without impacting theperformance observed by the existing users.

FIG. 4 is a block diagram depicting an example operating environment 400with multiple users accessing multiple databases through multiplevirtual warehouses. In environment 400, multiple users 402, 404, and 406access multiple databases 414, 416, 418, 420, 422, and 424 throughmultiple virtual warehouses 408, 410, and 412. Although not shown inFIG. 4 , users 402, 404, and 406 may access virtual warehouses 408, 410,and 412 through resource manager 102 (FIG. 1 ). In particularembodiments, databases 414-424 are contained in storage platform 114(FIG. 1 ) and are accessible by any virtual warehouse implemented inexecution platform 112. In some embodiments, users 402-406 access one ofthe virtual warehouses 408-412 using a data communication network, suchas the Internet. In some implementations, each user 402-406 specifies aparticular virtual warehouse 408-412 to work with at a specific time. Inthe example of FIG. 4 , user 402 interacts with virtual warehouse 408,user 404 interacts with virtual warehouse 410, and user 406 interactswith virtual warehouse 412. Thus, user 402 submits data retrieval anddata storage requests through virtual warehouse 408. Similarly, users404 and 406 submit data retrieval and data storage requests throughvirtual warehouses 410 and 412, respectively.

Each virtual warehouse 408-412 is configured to communicate with asubset of all databases 414-424. For example, in environment 400,virtual warehouse 408 is configured to communicate with databases 414,416, and 422. Similarly, virtual warehouse 410 is configured tocommunicate with databases 416, 418, 420, and 424. And, virtualwarehouse 412 is configured to communicate with databases 416, 422, and424. In alternate embodiments, one or more of virtual warehouses 408-412communicate with all of the databases 414-424. The arrangement shown inFIG. 4 allows individual users to send all data retrieval and datastorage requests through a single virtual warehouse. That virtualwarehouse processes the data retrieval and data storage tasks usingcached data within one of the execution nodes in the virtual warehouse,or retrieves (and caches) the necessary data from an appropriatedatabase. The mappings between the virtual warehouses is a logicalmapping, not a hardware mapping. This logical mapping is based on accesscontrol parameters related to security and resource access managementsettings. The logical mappings are easily changed without requiringreconfiguration of the virtual warehouse or storage resources.

Although environment 400 shows virtual warehouses 408-412 configured tocommunicate with specific subsets of databases 414-424, thatconfiguration is dynamic. For example, virtual warehouse 408 may bereconfigured to communicate with a different subset of databases 414-424based on changing tasks to be performed by virtual warehouse 408. Forinstance, if virtual warehouse 408 receives requests to access data fromdatabase 418, virtual warehouse 408 may be reconfigured to alsocommunicate with database 418. If, at a later time, virtual warehouse408 no longer needs to access data from database 418, virtual warehouse408 may be reconfigured to delete the communication with database 418.

FIG. 5 is a block diagram depicting another example operatingenvironment 500 with multiple users accessing multiple databases througha load balancer and multiple virtual warehouses contained in a virtualwarehouse group. Environment 500 is similar to environment 400 (FIG. 4), but additionally includes a virtual warehouse resource manager 508and multiple virtual warehouses 510, 512, and 514 arranged in a virtualwarehouse group 516. Virtual warehouse resource manager 508 may becontained in resource manager 102. In particular, multiple users 502,504, and 506 access multiple databases 518, 520, 522, 524, 526, and 528through virtual warehouse resource manager 508 and virtual warehousegroup 516. In some embodiments, users 502-506 access virtual warehouseresource manager 508 using a data communication network, such as theInternet. Although not shown in FIG. 5 , users 502, 504, and 506 mayaccess virtual warehouse resource manager 508 through resource manager102 (FIG. 1 ). In some embodiments, virtual warehouse resource manager508 is implemented within resource manager 102.

Users 502-506 may submit data retrieval and data storage requests tovirtual warehouse resource manager 508, which routes the data retrievaland data storage requests to an appropriate virtual warehouse 510-514 invirtual warehouse group 516. In some implementations, virtual warehouseresource manager 508 provides a dynamic assignment of users 502-506 tovirtual warehouses 510-514. When submitting a data retrieval or datastorage request, users 502-506 may specify virtual warehouse group 516to process the request without specifying the particular virtualwarehouse 510-514 that will process the request. This arrangement allowsvirtual warehouse resource manager 508 to distribute multiple requestsacross the virtual warehouses 510-514 based on efficiency, availableresources, and the availability of cached data within the virtualwarehouses 510-514. When determining how to route data processingrequests, virtual warehouse resource manager 508 considers availableresources, current resource loads, number of current users, and thelike.

In some embodiments, fault tolerance systems create a new virtualwarehouses in response to a failure of a virtual warehouse. The newvirtual warehouse may be in the same virtual warehouse group or may becreated in a different virtual warehouse group at a different geographiclocation.

Each virtual warehouse 510-514 is configured to communicate with asubset of all databases 518-528. For example, in environment 500,virtual warehouse 510 is configured to communicate with databases 518,520, and 526. Similarly, virtual warehouse 512 is configured tocommunicate with databases 520, 522, 524, and 528. And, virtualwarehouse 514 is configured to communicate with databases 520, 526, and528. In alternate embodiments, virtual warehouses 510-514 maycommunicate with any (or all) of the databases 518-528.

Although environment 500 shows one virtual warehouse group 516,alternate embodiments may include any number of virtual warehousegroups, each associated with any number of virtual warehouses. Thenumber of virtual warehouse groups in a particular environment isdynamic and may change based on the changing needs of the users andother systems in the environment.

FIG. 6 is a block diagram depicting another example operatingenvironment 600 having multiple distributed virtual warehouses andvirtual warehouse groups. Environment 600 includes resource manager 102that communicates with virtual warehouse groups 604 and 606 through adata communication network 602. Warehouse group 604 includes two virtualwarehouses 608 and 610, and warehouse group 606 includes another twovirtual warehouses 614 and 616. Resource manager 102 also communicateswith virtual warehouse 612 (which is not part of a virtual warehousegroup) through data communication network 602.

Virtual warehouse groups 604 and 606 as well as virtual warehouse 612communicate with databases 620, 622, and 624 through a datacommunication network 618. In some embodiments data communicationnetworks 602 and 618 are the same network. Environment 600 allowsresource manager 102 to coordinate user data storage and retrievalrequests across the multiple virtual warehouses 608-616 to store andretrieve data in databases 620-624. Virtual warehouse groups 604 and 606can be located in the same geographic area, or can be separatedgeographically. Additionally, virtual warehouse groups 604 and 606 canbe implemented by the same entity or by different entities.

The systems and methods described herein allow data to be stored andaccessed as a service that is separate from computing (or processing)resources. Even if no computing resources have been allocated from theexecution platform, data is available to a virtual warehouse withoutrequiring reloading of the data from a remote data source. Thus, data isavailable independently of the allocation of computing resourcesassociated with the data. The described systems and methods are usefulwith any type of data. In particular embodiments, data is stored in astructured, optimized format. The decoupling of the data storage/accessservice from the computing services also simplifies the sharing of dataamong different users and groups. As discussed herein, each virtualwarehouse can access any data to which it has access permissions, evenat the same time as other virtual warehouses are accessing the samedata. This architecture supports running queries without any actual datastored in the local cache. The systems and methods described herein arecapable of transparent dynamic data movement, which moves data from aremote storage device to a local cache, as needed, in a manner that istransparent to the user of the system. Further, this architecturesupports data sharing without prior data movement since any virtualwarehouse can access any data due to the decoupling of the data storageservice from the computing service.

FIG. 7 is a flow diagram depicting an embodiment of a method 700 formanaging data storage and retrieval operations. Initially, method 700receives a statement, request or query from a user at 702. A statementis any request or command to perform a data-related operation. Examplestatements include data retrieval requests, data storage requests, datatransfer requests, data queries, and the like. In some embodiments, thestatement is implemented as an SQL statement. A resource manager createsa query coordinator at 704 to manage the received statement. Forexample, the query coordinator manages the various tasks necessary toprocess the received statement, including interacting with an executionplatform and one or more data storage devices. In some embodiments, thequery coordinator is a temporary routine created specifically to managethe received statement.

Method 700 continues as the resource manager determines multiple tasksnecessary to process the received statement at 706. The multiple tasksmay include, for example, accessing data from a cache in an executionnode, retrieving data from a remote storage device, updating data in acache, storing data in a remote storage device, and the like. Theresource manager also distributes the multiple tasks to execution nodesin the execution platform at 708. As discussed herein, the executionnodes in the execution platform are implemented within virtualwarehouses. Each execution node performs an assigned task and returns atask result to the resource manager at 710. In some embodiments, theexecution nodes return the task results to the query coordinator. Theresource manager receives the multiple task results and creates astatement result at 712, and communicates the statement result to theuser at 714. In some embodiments, the query coordinator is deleted afterthe statement result is communicated to the user.

FIG. 8 is a flow diagram depicting an embodiment of a method 800 formanaging a data cache. Initially, method 800 receives (or identifies) aquery from a user at 802. Method 800 identifies multiple files necessaryto process the received query at 804. To process the multiple files atsubstantially the same time, each of the multiple files are distributedto a particular execution node for processing at 806. In particularembodiments, any number of execution nodes are used to process themultiple files. Each of the execution nodes are instructed to executethe query at 808 based on the files distributed to that execution node.

Method 800 continues as each execution node determines at 810 whetherthe files distributed to the execution node are stored in the executionnode's cache. The execution node's cache may also be referred to as a“local cache.” If the files are already stored in the execution node'scache, the execution node processes the query using those cached filesat 816. However, if one or more of the files are not stored in theexecution node's cache, the execution node retrieves the non-cachedfiles from a remote storage device at 812. The execution node stores theretrieved files in the local cache at 814, and processes the query usingthe retrieved files at 816. In some embodiments the execution nodemodifies the retrieved file prior to storing the file in the localcache. For example, the execution node may decrypt an encrypted file ordecompress a compressed file. By decrypting or decompressing the fileprior to caching, the execution node only performs that modificationonce, instead of decrypting or decompressing the file each time it isaccessed from the local cache.

After processing the query, the execution node updates metadatainformation based on the current state of the local cache at 818.Metadata 110 (FIG. 1 ) stores information about data cached in eachexecution node. Thus, each time data in an execution node is updated(e.g., new data is cached or data is moved from a fast memory to aslower HDD), metadata 110 is updated to reflect the execution nodeupdate.

In some embodiments, the received query contains a single instruction.That single instruction is implemented by each of the multiple executionnodes at substantially the same time. Although each of the multipleexecution nodes are implementing the same instruction, each executionnode is responsible for different files on which the instruction isimplemented. Thus, the single instruction is implemented on multipledifferent data files by the multiple execution nodes in parallel withone another.

The example systems and methods described herein provide a distributedcache architecture within a single virtual warehouse or across multiplevirtual warehouses. Each execution node in a particular virtualwarehouse has its own cache. The multiple execution nodes in theparticular virtual warehouse form a distributed cache (i.e., distributedacross the multiple execution nodes). In other embodiments, the cachemay be distributed across multiple execution nodes contained in multipledifferent virtual warehouses.

In some implementations, the same file is cached by multiple executionnodes at the same time. This multiple caching of files helps with loadbalancing (e.g., balancing data processing tasks) across multipleexecution nodes. Additionally, caching a file in multiple executionnodes helps avoid potential bottlenecks when significant amounts of dataare trying to pass through the same communication link. Thisimplementation also supports the parallel processing of the same data bydifferent execution nodes.

The systems and methods described herein take advantage of the benefitsof both shared-disk systems and the shared-nothing architecture. Thedescribed platform for storing and retrieving data is scalable like theshared-nothing architecture once data is cached locally. It also has allthe benefits of a shared-disk architecture where processing nodes can beadded and removed without any constraints (e.g., for 0 to N) and withoutrequiring any explicit reshuffling of data.

In some embodiments, one or more of the caches contained in theexecution nodes are multi-level caches that include different types ofdata storage devices. For example, a particular cache may have ahierarchy of data storage devices that provide different data accessspeeds. In one embodiment, a cache includes memory that provides thefastest data access speed, a solid-state drive (SSD) that providesintermediate data access speed, and a hard disk drive (HDD) thatprovides slower data access speed. Resource manager 102 (FIG. 1 ) and/orother systems can manage which data is stored in the different datastorage devices. For example, the most frequently accessed data isstored in the memory and the least frequently accessed data is stored inthe hard disk drive. In some embodiments, a least-recently used (LRU)algorithm is utilized to manage the storage of data in the multiplestorage devices. For example, the LRU algorithm may determine whether tostore particular data in a fast memory or a slower storage device. Insome implementations, the LRU algorithm also determines which data toremove from a cache.

In some embodiments, only a portion of certain files are cached. Forexample, when data is stored in a columnar format and only certaincolumns within the file are being accessed on a regular basis, thesystem may choose to cache the columns being accessed (and not cache theother columns). This approach preserves the cache storage space andprovides an effective use of the available cache resources.Additionally, this approach reduces the amount of data that is copiedfrom the remote storage devices to the cache. Rather than copying theentire file from the remote storage devices, only the relevant columnsare copied from the remote storage device into the cache. In otherembodiments, the described systems and methods cache certain rows withinthe file that are being accessed on a regular basis.

Additionally, the described systems and methods are able to prune out apiece of data when it is not relevant to a particular query withouthaving to first access that piece of data. For example, the systems andmethods minimize the amount of data loaded from a remote storage deviceby pruning both horizontally (the system knows the subset of rows thatneed to be accessed) and vertically (only the referenced columns areloaded). This is accomplished by storing the metadata (i.e., themetadata associated with the stored data) separately from the storeddata. This metadata allows the systems and methods to determine whichfiles (and which file pieces) need to be accessed for a particular task.

In some embodiments, the systems and methods described herein can save ametadata state associated with a particular cache. For example, themetadata state information may include a list of all files (or filepieces) stored in the cache and the last time each file (or file piece)was accessed. This metadata state information is saved when an executionnode or virtual warehouse is hibernated. Then, when the execution nodeor virtual warehouse is restored, the metadata state information is usedto prime the cache, thereby restoring the cache to the same state (i.e.,storing the same data files) as when the hibernation occurred. Usingthis approach, the cache does not need to be repopulated with data overa period of time based on assigned tasks. Instead, the cache isimmediately populated with data to restore the previous state withoutthe lag time of starting with an empty cache. This process may bereferred to as “warming the cache.”

The metadata discussed herein may include information regarding offsetsin a file. For example, the metadata may identify all pieces of aparticular file and include a map of the file (i.e., a map identifyingall pieces of the file). The metadata associated with the file piecesmay include a file name, a file size, a table to which the file belongs,a column size, a column location, and the like. The column location maybe expressed as a column offset (e.g., an offset from the beginning ofthe file). The column offset specifies a particular location within thefile. In some embodiments, this metadata is contained in the first fewbytes of a file header. Thus, the system can determine from the fileheader how to access the pieces of the file (using the map of the filedefined in the metadata) without having to access a metadata database(e.g., database 110 in FIG. 1 ).

In particular implementations, a cache may use multiple storage devices,such as memory and a local disk storage device. To maximize the cachehit rate, files (or portions of files) that have not been accessedrecently are removed from the cache to provide storage space for otherfiles (or portions of other files) that are being accessed morefrequently.

FIG. 9 is a block diagram depicting an example computing device 900. Insome embodiments, computing device 900 is used to implement one or moreof the systems and components discussed herein. For example, computingdevice 900 may allow a user or administrator to access resource manager102. Further, computing device 900 may interact with any of the systemsand components described herein. Accordingly, computing device 900 maybe used to perform various procedures and tasks, such as those discussedherein. Computing device 900 can function as a server, a client or anyother computing entity. Computing device 900 can be any of a widevariety of computing devices, such as a desktop computer, a notebookcomputer, a server computer, a handheld computer, a tablet, and thelike.

Computing device 900 includes one or more processor(s) 902, one or morememory device(s) 904, one or more interface(s) 906, one or more massstorage device(s) 908, and one or more Input/Output (I/O) device(s) 910,all of which are coupled to a bus 912. Processor(s) 902 include one ormore processors or controllers that execute instructions stored inmemory device(s) 904 and/or mass storage device(s) 908. Processor(s) 902may also include various types of computer-readable media, such as cachememory.

Memory device(s) 904 include various computer-readable media, such asvolatile memory (e.g., random access memory (RAM)) and/or nonvolatilememory (e.g., read-only memory (ROM)). Memory device(s) 904 may alsoinclude rewritable ROM, such as Flash memory.

Mass storage device(s) 908 include various computer readable media, suchas magnetic tapes, magnetic disks, optical disks, solid state memory(e.g., Flash memory), and so forth. Various drives may also be includedin mass storage device(s) 908 to enable reading from and/or writing tothe various computer readable media. Mass storage device(s) 908 includeremovable media and/or non-removable media.

I/O device(s) 910 include various devices that allow data and/or otherinformation to be input to or retrieved from computing device 900.Example I/O device(s) 910 include cursor control devices, keyboards,keypads, microphones, monitors or other display devices, speakers,printers, network interface cards, modems, lenses, CCDs or other imagecapture devices, and the like.

Interface(s) 906 include various interfaces that allow computing device900 to interact with other systems, devices, or computing environments.Example interface(s) 906 include any number of different networkinterfaces, such as interfaces to local area networks (LANs), wide areanetworks (WANs), wireless networks, and the Internet.

Bus 912 allows processor(s) 902, memory device(s) 904, interface(s) 906,mass storage device(s) 908, and I/O device(s) 910 to communicate withone another, as well as other devices or components coupled to bus 912.Bus 912 represents one or more of several types of bus structures, suchas a system bus, PCI bus, IEEE 1394 bus, USB bus, and so forth.

For purposes of illustration, programs and other executable programcomponents are shown herein as discrete blocks, although it isunderstood that such programs and components may reside at various timesin different storage components of computing device 900, and areexecuted by processor(s) 902. Alternatively, the systems and proceduresdescribed herein can be implemented in hardware, or a combination ofhardware, software, and/or firmware. For example, one or moreapplication specific integrated circuits (ASICs) can be programmed tocarry out one or more of the systems and procedures described herein.

Although the present disclosure is described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art, given the benefit of this disclosure,including embodiments that do not provide all of the benefits andfeatures set forth herein, which are also within the scope of thisdisclosure. It is to be understood that other embodiments may beutilized, without departing from the scope of the present disclosure.

The invention claimed is:
 1. A method comprising: receiving a querydirected to database data stored across a plurality of shared storagedevices; referencing a metadata store to locate a set of files thatcomprises data that needs to be processed to respond to the query;referencing the metadata store to determine whether the set of files iscached among execution nodes of an execution platform comprising aplurality of execution nodes, wherein the execution platform is separatefrom the metadata store and the plurality of shared storage devices; inresponse to determining that at least a portion of the set of files iscached among the plurality of execution nodes, assigning by one or moreprocessors, processing of one or more of the set of files to each of oneor more execution nodes that have cached at least a portion of the setof files; for each of the one or more assigned execution nodes:determining, by the assigned execution node, whether the assigned one ormore files is stored at least in part in a cache of the assignedexecution node; and in response to the assigned execution nodedetermining the assigned one or more files is not entirely stored in thecache of the assigned execution node: retrieving a missing portion ofthe assigned one or more files from one or more remote storage devicesof the plurality of remote storage devices including the missing portionof the assigned one or more files, wherein the plurality of executionnodes are organized into one or more virtual warehouses having one ormore logical mappings between them, and a virtual warehouse includingthe assigned execution node dynamically establishes a communication linkwith each of the one or more of the plurality of remote storage devicesbased at least in part on the query so that the assigned execution nodemay retrieve the missing portion; storing, by the assigned executionnode, the missing portion of the assigned one or more files in the cacheof the assigned execution node so that the entire one or more files isstored in the cache of the assigned execution node, wherein a size andcomposition of the cache is adjusted to accommodate the missing portionof the assigned one or more files; processing the query using theassigned one or more files stored in the cache of the assigned executionnode; and updating the metadata store to indicate the entire assignedone or more files is now cached in the cache of the assigned executionnode; wherein any of the set of files stored in the plurality of sharedstorage devices may be accessed by any of a plurality of execution nodesof the execution platform; wherein any of the set of files stored in theplurality of shared storage devices may be stored in a cache of any ofthe plurality of execution nodes of the execution platform; and whereinany of the set of files stored in the plurality of shared storagedevices may be stored in a cache of multiple execution nodes of theplurality of execution nodes of the execution platform at one point intime; and in response to a determination of a change in the number ofexecution nodes of the execution platform, wherein the change iscreating a new execution node, the new execution node comprising aplurality of processors, wherein the cache varies among the plurality ofprocessors, wherein a first subset of the plurality of processorscomprises a minimal cache and a second subset of the plurality ofprocessors comprises a cache providing faster input-output operations,reassign processing, among the changed number of execution nodes of theexecution platform, of the set of files comprising data that needs to beprocessed to respond to the query.
 2. The method of claim 1, furthercomprising: in response to the assigned execution node determining theassigned one or more files is entirely stored in the cache of theassigned execution node, processing, using one or more processors of theassigned execution node, the query using the assigned one or more filesstored in the cache of the assigned execution node.
 3. The method ofclaim 1, wherein updating the metadata store to indicate the entireassigned one or more files is now cached in the assigned execution nodecomprises updating the metadata store to identify all files that areduplicated in the cache of the assigned execution node.
 4. The method ofclaim 1, further comprising determining, by the assigned execution node,whether to store the assigned one or more files in faster or slowermemory by implementing a least recently used (LRU) algorithm.
 5. Themethod of claim 4, wherein implementing the LRU algorithm furthercomprises identifying one or more copies of the assigned one or morefiles to be removed from the cache.
 6. The method of claim 1, whereinthe metadata store is separate and independently scalable from each ofthe resource manager, the plurality of shared storage devices, and theexecution platform, and wherein the metadata store comprises a completemetadata listing of the database data stored across the plurality ofshared storage devices and a complete listing of files cached in theplurality execution nodes of the execution platform.
 7. The method ofclaim 1, wherein each execution node of the execution platform comprisesa cache, wherein the cache includes a first storage portion and a secondstorage portion, wherein the first storage portion is significantlyfaster than the second storage portion.
 8. The method of claim 1,wherein the query directed to the database data comprises a singleinstruction that is applied by the execution platform to each of the setof files substantially simultaneously.
 9. The method of claim 1, whereineach execution node of the plurality of execution nodes comprises atleast one processor and at least one local cache caching a copy of atleast a portion of the database data.
 10. The method of claim 1, furthercomprising: in response to the assigned execution node determining theassigned one or more files is not stored in the cache of the assignedexecution node, modifying, by the assigned execution node a databasedata structure of the retrieved copy of the assigned one or more filesprior to storing the retrieved copy in the cache.
 11. The method ofclaim 10, wherein modifying the database data structure of the retrievedcopy includes decrypting the retrieved copy.
 12. The method of claim 10,wherein modifying the database data structure of the retrieved copyincludes decompressing the retrieved copy.
 13. A system comprising: aplurality of shared storage devices collectively storing database data;a metadata store separate from the plurality of shared storage devices,the metadata store comprising metadata for the database data storedacross the plurality of shared storage devices; and one or moreprocessors operatively coupled to the metadata store, the one or moreprocessors to: receive a query directed to the database data storedacross the plurality of shared storage devices reference the metadatastore to locate a set of files that comprises data that needs to beprocessed to respond to the query; reference the metadata store todetermine whether the set of files is cached among execution nodes of anexecution platform comprising a plurality of execution nodes, whereinthe execution platform is separate from the metadata store and theplurality of shared storage devices; and in response to determining thatat least a portion of the set of files is cached among the plurality ofexecution nodes, assigning processing of one or more of the set of filesto each of one or more execution nodes that have cached at least aportion of the set of files; for each of the assigned execution nodes:determine, by the assigned execution node, whether the assigned one ormore files is stored at least in part in a cache of the assignedexecution node; and in response to the assigned execution nodedetermining the assigned one or more files is not entirely stored in thecache of the assigned execution node: retrieve a missing portion of theassigned one or more files from one or more of the plurality of remotestorage devices including the missing portion of the assigned one ormore files, wherein the plurality of execution nodes are organized intoone or more virtual warehouses having one or more logical mappingsbetween them, and a virtual warehouse including the assigned executionnode dynamically establishes a communication link with each of the oneor more of the plurality of shared storage devices based at least inpart on the query so that the assigned execution node may retrieve themissing portion; store, by the assigned execution node, the entireassigned one or more files in the cache of the assigned execution node,wherein a size and composition of the cache of the assigned executionnode is adjusted to accommodate the missing portion of the assigned oneor more files; process the query using the assigned one or more filesstored in the cache of the assigned execution node; and update themetadata store to indicate the entire assigned one or more files is nowcached in the cache of the assigned execution node; wherein any of theset of files stored in the plurality of shared storage devices may beaccessed by any of the plurality of execution nodes of the executionplatform; wherein any of the set of files stored in the plurality ofshared storage devices may be stored in a cache of any of the pluralityof execution nodes of the execution platform; and wherein any of the setof files stored in the plurality of shared storage devices may be storedin a cache of multiple execution nodes of the plurality of executionnodes of the execution platform at one point in time; and in response toa determination of a change in the number of execution nodes of theexecution platform, wherein the change is creating a new execution node,the new execution node comprising a plurality of processors, wherein thecache varies among the plurality of processors, wherein a first subsetof the plurality of processors comprises a minimal cache and a secondsubset of the plurality of processors comprises a cache providing fasterinput-output operations, reassign processing, among the changed numberof execution nodes of the execution platform, of the set of filescomprising data that needs to be processed to respond to the query. 14.The system of claim 13, wherein each execution node of the executionplatform comprises at least one local processor and at least one cache,wherein the at least one cache of each execution node comprises a memorydevice and a disk storage device.
 15. The system of claim 14, whereinthe one or more processors are further to: in response to the assignedexecution node determining the entire assigned one or more files isstored in the cache of the assigned execution node, processing the queryusing the assigned one or more files stored in the cache of the assignedexecution node.
 16. The system of claim 13, wherein each execution nodeof the execution platform is programmed to modify a data structureassociated with a copy of a particular file assigned thereto prior tostoring the copy in a cache thereof.
 17. A non-transitory computerreadable storage medium having instructions stored thereon that, whenexecuted by one or more processors, cause the one or more processors to:receive a query directed to database data stored across a plurality ofshared storage devices; reference a metadata store to locate a set offiles that comprises data that needs to be processed to respond to thequery; reference the metadata store to determine whether the set offiles is cached among execution nodes of an execution platformcomprising a plurality of execution nodes, wherein the executionplatform is separate from the metadata store and the plurality of sharedstorage devices; in response to determining that at least a portion ofthe set of files is cached among the plurality of execution nodes,assigning by the one or more processors, processing of one or more ofthe set of files to each of one or more execution nodes that have cachedat least a portion of the set of files; for each of the assignedexecution nodes: determining, by the assigned execution node, whetherthe assigned one or more files is stored at least in part in a cache ofthe assigned execution node; and in response to the assigned executionnode determining the assigned one or more files is not entirely storedin the cache of the assigned execution node: retrieving a missingportion of the assigned one or more files from one or more remotestorage devices of the plurality of remote storage devices that includethe missing portion, wherein the plurality of execution nodes areorganized into one or more virtual warehouses having one or more logicalmappings between them, and a virtual warehouse that includes theassigned execution node dynamically establishes a communication linkwith each of the one or more of the plurality of shared storage devicesbased at least in part on the query so that the assigned execution nodemay retrieve the missing portion; storing, by the assigned executionnode, the entire assigned one or more files in the cache of the assignedexecution node, wherein a size and composition of the cache of theassigned execution node is adjusted to accommodate the missing portionof the assigned one or more files; processing the query using theassigned one or more files stored in the cache of the assigned executionnode; and updating the metadata store to indicate the entire assignedone or more files is now cached in the cache of the assigned executionnode; wherein any of the set of files stored in the plurality of sharedstorage devices may be accessed by any of a plurality of execution nodesof the execution platform; wherein any of the set of files stored in theplurality of shared storage devices may be stored in a cache of any ofthe plurality of execution nodes of the execution platform; and whereinany of the set of files stored in the plurality of shared storagedevices may be stored in a cache of multiple execution nodes of theplurality of execution nodes of the execution platform at one point intime; and in response to a determination of a change in the number ofexecution nodes of the execution platform, wherein the change iscreating a new execution node, the new execution node comprising aplurality of processors, wherein the cache varies among the plurality ofprocessors, wherein a first subset of the plurality of processorscomprises a minimal cache and a second subset of the plurality ofprocessors comprises a cache providing faster input-output operations,reassign processing, among the changed number of execution nodes of theexecution platform, of the set of files comprising data that needs to beprocessed to respond to the query.
 18. The non-transitory computerreadable storage media of claim 17, wherein the database query statementcomprises a single instruction that is applied by the plurality ofexecution nodes to applicable files of database data substantiallysimultaneously.
 19. The non-transitory computer readable storage mediaof claim 18, wherein the one or more processors are further to: inresponse to the assigned execution node determining the assigned one ormore files is entirely stored in the cache of the assigned executionnode, process the query using the assigned one or more files stored inthe cache of the assigned execution node.
 20. The non-transitorycomputer readable storage media of claim 17, wherein each execution nodeof the execution platform comprises at least one local processor and atleast one cache, wherein the at least one cache of each execution nodecomprises a memory device and a disk storage device.
 21. Thenon-transitory computer readable storage media of claim 17, wherein eachexecution node of the execution platform is programmed to modify a datastructure associated with a copy of a particular file assigned theretoprior to storing the copy in a cache thereof.